1. Field of the Invention
The present disclosure relates to an optical pickup and optical read/write apparatus which writes information on an optical storage medium such as an optical tape and read the information being written in parallel.
2. Description of the Related Art
An optical tape drive system which performs read and write operations on an optical tape medium using a plurality of optical pickups at the same time by utilizing a high density optical recording technique has been proposed as an optical read/write apparatus that can be used effectively for the purpose of bulk data archival and storage. Japanese Laid-Open Patent Publication No. 2006-286070 (which will be referred to herein as “Patent Document No. 1” for convenience sake) discloses an example of such an optical tape drive system.
Meanwhile, in a conventional magnetic tape drive system, a write head and a read head are arranged separately with respect to a track on which data is going to be written. And by writing data and reading the data being written simultaneously, verification can be made to see if the data has been written just as intended. In this manner, high speed processing can get done with a sufficiently high degree of reliability ensured.
It is known that such a verify technology is also applicable to an optical read/write apparatus that is designed to read and write data from/on a disc medium such as a magneto-optical (MO) disc, a Blu-ray Disc (BD), a DVD or a CD using an optical pickup. According to such a technology, a light beam that has been emitted from a laser light source is split through a diffraction grating into a zero-order light beam and ±first-order light beams, with which a storage layer is irradiated. In this case, a write operation can be performed by irradiating the storage layer with the zero-order light beam and a verify operation can be performed by detecting the ±first-order light beams. Such a technology is called a DRAW (direct read after write) technology. According to such a technology, an error check can be made right after data has been written, and therefore, the processing can get done quickly and the transfer rate can be increased. A read/write apparatus that adopts the DRAW technology is disclosed in Japanese Laid-Open Patent Publication No. 6-162532 (which will be referred to herein as “Patent Document No. 2” for convenience sake), for example.
An optical read/write apparatus needs to perform a focus control and a tracking control appropriately during read and write operations. Particularly when an optical tape is used as an optical storage medium, the tracking control needs to be performed in accordance with the properties of the tracks of the optical tape, which are different from those of a normal optical disc.
Examples of known tracking control methods for optical disc drives include the push-pull (PP) method, the advanced push-pull (APP) method, and the correct far field (CFF) method, which are disclosed in Patent Document No. 2 and Japanese Laid-Open Patent Publications No. 8-306057 and No. 2000-306262 (which will be referred to herein as “Patent Documents Nos. 3 and 4”, respectively, for convenience sake), respectively.
However, none of these known optical read/write apparatuses can obtain a tracking signal that is suitably used in an optical storage medium such as an optical tape where the tracking position may change significantly during reading or writing.
Thus, the present disclosure provides an optical read/write apparatus that can stabilize the tracking performance even when dealing with an optical storage medium such as an optical tape where the track position may change significantly during the operation.